1. Field of the invention
The invention relates to a method and a device for positioning a clamping device for workpieces within a predetermined working space.
The invention is described hereafter essentially with reference to a measuring machine and a positioning and clamping system provided for it, but is not restricted to measuring machines of this kind, instead being capable of being used in the same way for positioning systems with the aid of triaxially controllable robot systems for a tool. The system is, to that extent, suitable both for measuring machines and for processing machines.
2. Discussion of the Prior Art
Workpieces of any contour, in order to be accurately measured or processed, must be temporarily fixed within a specific three-dimensional space corresponding to the range of the measuring system or processing machine. Where measuring machines are concerned, this space is delimited in the plane by a measuring plate, a measuring table or a clamping plate, and the third dimension is determined by the range of the measuring tracer on a measuring bridge or a measuring boom (DE 22 32 858 A2 and DE 37 17 541 A1).
Adjustable columns, which can be locked with pin-point accuracy on the clamping plate, serve as clamping devices or seating columns for the workpiece. These include devices, such as are known, for example, from DE 44 24 765 A1 or U.S. Pat. No. 4,848,005.
A complete software-controlled measuring machine "TYPHOON" with a "Five Unique" clamping device was published in a prospectus of the same name by the company DEA-Brown-Sharpe SpA, Moncalieri, IT.
With the aid of the measuring machines or measuring robot, a reference point corresponding to a clamping point of the workpiece is approached in the three-dimensional measuring space surrounding the workpiece. A support or clamping column, which can be fixed on the measuring table, is then placed under this clamping point, as a rule by displacing the column as accurately as possible, manually or mechanically (U.S. Pat. No. 4,848,005), in the horizontal plane (XY-axis) and adjusting its height (Z-axis) vertically. The other clamping points are found and fixed in the same way.
A CAD program or a drawing of the workpiece, which are edited for software processing in the measuring machine, serves as an aid. In addition, the measuring rod or tracer of the measuring machine is replaced by a removable centering device which serves as a complementary simulated workpiece point at the clamping point of the column to be positioned. The centering device has a coupling element, for example a gripper or a ball catch, so that the column to be positioned can be coupled positively. This complicated positioning method is described in detail in DE 195 10 456 A1, as are some clamping means which can be used for fixing the workpieces.
Turntables with positioning accuracies of below +/-0.05.degree. absolute accuracy, which are equipped with stepping motors or servomotors, are also known for positioning components at specific angles in one plane. The positioning accuracy is achieved by means of limit switches which utilize the Hall effect. Turntables of this kind bearing the type designation RTM are offered by the company Spindler & Hoyer GmbH & Co, Gottingen, Del.
Measuring columns movable on a measuring plate may be used, according to EP-B-0,216,041 for the automatic detection of individual measuring points even of very large components.
It is not possible, with the systems mentioned, to simulate a seating surface of any position and extent in the three-dimensional measuring space, that is to say working space, or to provide for a seating surface of this kind a column with a plane or curved clamping surface or otherwise spatial clamping surface; at least not when the position of the surface in the space assumes any solid angle which deviates from the angles standardized in grid systems, such as 15.degree., 30.degree., 45.degree., etc.
As regards the details of the clamping elements, centering balls and other details of the measuring machine, measuring plate and columns for the workpiece seatings and their functioning, reference is made to the publications mentioned here, and the description of these, by being quoted, is included in the disclosure of this invention. This applies insofar as other systems are not described for preference here.